Greases based on finely divided inorganic material



?atented Oct. 21 1952 GREASES BASED ON FINELY DIVIDE D INORGANICMATERIAL Alan Beerbower, Baltimore, Mil, and Arnold J. Morway, Clark, N.J assignors to Standard Oil Development Company, a corporation ofDelaware No Drawing. Application November 12, 1948, Serial No. 59,748

Claims.

The present invention relates to greases thickened with finely dividedinorganic materials, and, in particular, to lubricating greases havinghigh melting points prepared from lubricating oil and light coloredfinely divided inorganic materials such as magnesium oxides andcarbonates.

- In the prior art, lubricating greases have ordinarily been composed ofa soap-thickened oil, particularly a mineral base lubricating oil,thickened to a pasty or solid consistency with about 3 to 25% or more ofmetal soaps of fatty materials. Soaps such as calcium stearate, sodiumstearate, and like compositions, prepared from fatty acids and/orvegetable or animal fats, have ordinarily been considered the mostsuitable thickening materials for lubicating greases. By their use,lubricating oils of a chosen consistency or viscosity may be gelled orsolidified so that the lubricant may remain in place and not run or leakaway from the point where lubrication is desired. The lubricatingproperties are de-' termined in large measure by the grade, viscosity,etc., of the oil, the filler or thickener serving mainly to solidify thematerial and keep the oil available at the point of lubrication to carryout its intended function.

Instead of soap thickeners, various substitutes have recently beendeveloped which have certain desirable features for such uses. Thus,greases have been prepared from lubricating oils and carbon black ofhigh oil absorptivity or so-called high structure index. The reticulatedor chainlike particled carbon blacks such as acetylene black have beenfound in the prior art to be excellent materials for this purpose.

Other inorganic materials such as bentonite and silica gels have beenproposed as the thickening agents for lubricating oils. Some of theseare unduly abrasive and, therefore, not very satisfactory, and others,such as the carbon blacks, are objectionable from the standpoint ofworkmen because of their extreme blackness and tendency to stain handsand clothing excessively. In addition, there ar numerous instances wherealight colored grease is preferred, for-example, where grease is likelyto drip and discolor material being worked on or where itis desirable tobe able to observe the functioning of lubricating parts which would beobscured by a black or highly colored grease.

It is, therefore, an object of the present invention to prepare alubricating grease of light color, approaching the color of the oil andhaving either a good degree of trasparency or a light color approachingwhite. Certain inorganic substances, of which the oxides and carbonatesof magnesium are particularly desirable, have the light coloredcharacteristics desired and according to the present invention are foundto be suitable grease-thickenihg agents. They are extremely porous andhence have high oil absorptivity. They are finely subdivided instructure so as to be quitefree of abrasive properties and they possessthe property of thickening lubricating oils to grease consistencies inreasonably small concentrations. They may be used either with mineralbase lubricating oils or with synthetic oils such as esters of dibasicacids polyalcohol oils, silicone polymer oils, and the like. Theseinorganic compounds are not used as saponifying agents in the presentcase, but are used as unneutralized thickeners.

The substantially unneutralized oxides an carbonates of magnesium appearto be particularly suitable for the purposes of the present inventionbecause of the peculiar position of mag nesium in the periodic table.Magnesium is the transition element between relatively alkaline andrelatively amphoteric elements of the alkaline earth group. Calcium andzinc oxides, which are below magnesium in this group, have been, used ingreases, but magnesium oxide appears to be much superior to either inits capacity to hold oil, and hence in its grease thickening capacity.Proportions of 10 to 25%, by weight for example, of magnesium oxide orcarbonate, thicken oils effectively to grease consistencies, whereasproportions of as much as 50 to of either the zincor the calcium oxidesor carbonates are required for similar thickening or grease; formingeffect. i

The magnesium compounds further appear to have outstandingproperties inbeing lubricants of themselves, whereas the corresponding cal-' ciumcompounds are too abrasive and also too reactive chemically forlubricating metal bearings. It should be emphasized that themagnesiumoxides and carbonates used in the presentinvention are not neutralizedwith fats or'fatty acids. They are to be distinguished, therefore,

from compositions which include magnesium soaps of fatty or othersaponifiable materials.

In general, a grease of the type to which this invention relatesconsists of a suitable lubricating oil having a viscosity which may beas low as 35 S. S. U. at F. or as high as 1,000 S. S. U. at the sametemperature. The oils may have any suitable viscosity index, but in viewof the fact that the greases in question are particularly suitable forhigh temperature use, oils of fair- 1y high viscosity index may bepreferred. The concentrations of the inorganic material may vary ratherwidely from as little as about 5% to as much as about 40% by weight,based on the finished lubricant. A grease of the general consistency ofNLGI grade #2 may be prepared by adding to of either unneutralized MgOor MgCO3. The preferred range is usually between 10 and of the fillermaterial. Greases of other consistencies can be prepared by varying theamount of filler or thickener and also to some extent by the choice oflubricating oil. In general, the term grease in this specification isintended to refer to a solid lubricant of true colloidal or gel-likecharacter, that is, a composition having an ASTM penetration, whenworked, of less than 390 mm./ 10. Usually a still lower penetrationnumber is obtained. The compositions of this invention thus are not tobe confused with liquid lubricants which contain mere suspensions ofinorganic materials. The invention will be more fully understood byreference to the following specific example.

Example A lubricating grease was prepared by milling together 18% byweight of a light oxide such as Bakers light magnesium oxide and aColombian distillate of 300 S. S. U. viscosity at 100 F. (50 at 210 F.).The oil was added slowly to the oxide while milling proceeded. Theresulting grease showed a worked penetration of 243 mm./10 by the ASTMtest method. The lubricant was tested by running it in the Shell FourBall Machine and was found to produce less wear than several compoundedmineral oils containing a polybutene thickener commonly used to imparttacky or adhesive properties to greases. The material prepared was alsorun in the A. B. E. C. machine for 24 hours at 3500 R. P. M. Nonoticeable wear was found in the 204 8-ball single race bearing whichwas used in this test or separation of oil from the inorganic thickener.The melting point of the grease was considerably above 500 F. and was infact above the evaporation point of the oil used.

Other magnesium oxides which are available commercially'were tested inthe same manner as that described in the example. It was found that thevery light materials were most satisfactory, those having bulk densitiesof more than about 2 lbs/gallon being somewhat unsatisfactory in thatexcessive amounts were required to obtain a desired grease consistencyor hardness. Various magnesium carbonates were also tested and thesefollowed the same general rule. Greases prepared from the lightermagnesium carbonates appeared to be slightly superior to those preparedfrom the oxides. The choice between using magnesium oxide and magnesiumcarbonate may depend in part upon the desired alkalinity of the finishedproduct. The oxides, of course, are more highly alkaline and for thisreason greases prepared from them may be considered undersirable forsome uses. Such alkalinity can be overcome, at least in part, by

partially neutralizing the oxides, as by adding moderate amounts offatty acids but these of course result in the production of soaps whichare likely to have fairly low melting points and to render the greaseless satisfactory for high temperature use if appreciable quantities ofsoaps are present.

The carbonates are more nearly neutral, although they may also reactwith saponifiable materials to produce some soap products. Wherealkalinity is objectionable, the carbonates usually may be found to besuperior.

It will be understood that the compositions of this invention maycomprise from 60 to about by weight of a suitable lubricating oil whichmay be a mineral base oil or a synthetic oil, together with as much as40% to as little as 5% of the thickener, based on the weight of thefinished product. The narrower ranges of 10 to 25% are usuallypreferred, calculated on the basis of the unneutralized inorganicmaterial. The base oils may contain various modifiers such asanti-oxidants, extreme pressure compounds, tackiness agents, viscosityindex improvers, rust inhibitors, sludge or corrosion inhibitors, andthe like. They may be added to the finished grease rather than beingadded to the oil as desired, as is well understood in the art.

What is claimed is:

l. A solid grease composition consisting essentially of a mineral baselubricating oil of 35 to 1000 S. S. U. viscosity at F. thickened to agrease consistency with 10 to 25% by weight of a finely dividedinorganic material having a bulk density of less than 2 lbs/gallon inits normal finely divided dry condition, said inorganic material beingselected from the group consisting of magnesium oxide and magnesiumcarbonate.

2. A composition as in claim 1 wherein the thickening agent is magnesiumoxide.

3. A composition as in claim 1 wherein the thickening agent is magnesiumcarbonate.

4. A solid lubricating grease comprising a mineral base lubricating oilof 35 to 1000' viscosity at 100 F. containing 10 to 25% by weight, basedon the total composition, of finely divided magnesium oxide.

5. Composition as in claim 4 wherein said magnesium oxide comprisesabout 18% of the weight of'the total composition.

' ALAN BEERBOWER.

ARNOLD J. MORWAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Chesny Mar. 11, 1941

1. A SOLID GREASE COMPOSITION CONSISTING ESSENTIALLY OF A MINERAL BASELUBRICATING OIL OF 35 TO 1000 S. S. U. VISCOSITY AT 100* F. THICKENED TOA GREASE CONSISTENCY WITH 10 TO 25% BY WEIGHT OF A FINELY DIVIDEDINORGANIC MATERIAL HAVING A BULK DENSITY OF LESS THAN 2 LBS./GALLON INITS NORMAL FINELY DIVIDED DRY CONDITION, SAID INORGANIC MATERIAL BEINGSELECTED FROM THE GROUP CONSISTING OF MAGNESIUM OXIDE AND MAGNESIUMCARBONATE.